Table 1. The four binomial outcomes possible in this McNemar’s test ^a .

	Control has risk allele(s)	Control lacks risk allele(s)	Row totals
Case has risk allele(s)	( +, +) a	( +, -) b	a + b
Case lacks risk allele(s)	( -, +) c	( -, -) d	c + d
	a + c	b + d	n

^a Each binomial outcome is a case-control pair, i.e., (case, control) with the sign indicating the presence or absence of the risk allele. For example, (+,-) indicates an informative outcome where the case has the risk allele and the control does not. The uninformative pairs are (+,+) and (-,-) where each member of the pair has identical risk allele status. Note that this table can be set up for scenarios of 1, 1 or 2, and 2 copies of risk alleles.